Manufacture of steel

ABSTRACT

A method for refining a molten metal particularly steel which includes the steps of placing a hood in the closed position over and in contact with a refining vessel, introducing a stream of oxygen/carbonaceous fuel such as fuel oil into the space below the hood and above the molten metal, igniting the oxygen/carbonaceous fuel stream with the hood located in said closed position over the refining vessel and the drawing off of resulting gases through the hood to a gas washer.

United States Patent 72] Inventor Hugh Willmott Grenfell 3,232,7482/1966 Rinesch 266/34 Glamorgan, South Wales 3,241,825 3/1966 Jilek eta1... 266/34 I21] Appl. No. 707,623 3,271,130 9/1966 Denig 266/34 [22]Filed Feb. 23, 1968 3,313,535 4/1967 Hopkins. 266/34 [45] Patented Aug.17, 1971 3,358,983 12/1967 Wegscheider et al. 266/31 [73] Assignee TheSteel Company of Wales Limited 3,377,158 4/1968 Meyer et a1 266/35Glamorgan, South Wales FOREIGN PATENTS Pmmy 22:3 :32: 772,632 4/1957Great Britain 266/35 8737/67 1,021,099 2/1966 Great Britain 266/34Primary Examiner-Gerald A. Dost Attorney-Krafft and Wells [54]MANUFATURE OF STEEL 10 Claims, 4 Drawing Figs.

[52] US. Cl 266/35, ABSTRACT: A method for fi i a molten meta] pal-cw75/60 266/34 LY 266/31 larly steel which includes the steps of placing ahood in the [5 ll."-

l d iti over d i o ta t a refining vessel in- Fleld 0 Search 27, t d i at am of o y en/carbonaceous fuel such as fuel 35, 34-1; 75/59, 60 oilinto the space below the hood and above the molten metal, igniting theoxygen/carbonaceous fuel stream with the hood [56] References cuedlocated in said closed position over the refining vessel and the UNITEDSTATES PATENTS drawing off of resulting gases through the hood to a gas3,026,102 3/1962 McFeaters 266/35 washer.

PRESSURE 5 105 mg m HINT/Milt g fl/H I l m m n l I PRESSURE MNTRULLER'AMT INVENTOR Hugh Wi/lmoif Grenfell B Kn/ 1v 211M )1 ATTORNEYS PATENTEDAUG 1 719m SHEET 2 OF 2 III INVENTOR Hugh Willmaff Grenfe/l 13 701% H20% ATTORNEYJS MANUFACTURE OF STEEL This invention relates to themanufacture of steel and is concerned particularly with the removal ofthe waste gases in unburned state from a steelmaking vessel such as aconverter.

In particular, the invention relates to the process of manufacturingsteel in a converter in which oxygen or an oxygenenriched mixture isblown therein from the top of the converter. In such a process it isnecessary to remove in some way during the process the unburned wastegases, and various gas cleaning and recovery systems have been suggestedwhich greatly reduce the normal pollution of the air associated withoxygen blend converters which is caused by ion oxide particles issuingas reddish-brown fumes with the refining gases.

One such gas cleaning and recovery system involves and use of avertically movable hood having a skirt which is mounted above the mouthof the converter and which, after ignition has taken place, is movableinto a position in engagement with or closely adjacent the mouth of theconverter. In such a known system there is at the beginning of the blowmuch unreacted oxygen present in the waste gases due to delay in thedecarburation reaction in the molten iron. Great care must therefore betaken to ensure that the oxygen content does not increase beyond the COnitrogen, into hazard limit and this risk is usually avoided by theinjection of an inert gas such as nitrogen, into the system to dilutethe waste gases at this critical time. In addition, the ingress ofadditional air from the atmosphere into the hood may be reduced by themaintaining of a predetermined pressure in the zone of the skirt of thehood and this is usually done by means of a pressure-sensitive controlwhich adjusts a venturi or other flow-restricting device in the ductingof the gas removal system.

From the foregoing, it will be appreciated that known gas recovery andcleaning systems for converters are not only hazardous in operation butcomplicated and cumbersome in use. The present invention, therefore, hasfor its object the provision of a greatly simplified system which avoidsthe above-mentioned disadvantages of the known system.

According to the present invention there is provided a method forrefining a molten metal which includes the steps of placing a hood in aclosed position over and in contact with a refining vessel such as aladle or converter containing the molten metal, introducing a stream ofoxygen and carbonaceous fuel into the space below the hood and above themolten metal, igniting the oxygen/carbonaceous fuel stream with the hoodlocated in said closed position over the refining vessel and drawing offthe resulting gases through the hood to a gas washer.

The converter may be operated in accordance with the par ticular methoddescribed more particularly in our copending U.S. Pat. Applications Nos.615,310, filed Feb. 13, 1967; 671,186, filed Sept. 25, 1967 and theapplication of Hugh Willmott Grenfell entitled Lance with Venturi,Oxygen Nozzle,filed Feb. 12, 1968.

The operation of a refining vessel or converter in this manner using anoxygen/carbonaceous fuel mixture enables a very simple gas removalsystem to be provided due primarily to the lack or considerablereduction of fume and to improve ignition. The ignition of the stream ofcarbonaceous fuel and oxygen mixture takes place with the hood closedthe process may be viewed during the process by, for instance, atelevision camera to determine the end point of the blow without openingthe hood.

The invention also provides apparatus for the refining of molten metalswhich comprises in combination a refining vessel, a hood connected tothe end of a gas exhaust duct disposed over an aperture in said vessel,sealing means provided for connecting the aperture and hood to preventsubstantial escape of gases passing from the vessel to the hood and oneor more nozzles disposed within said vessel and adapted to provide astream of oxygen and carbonaceous fuel, the arrangement being such thatthe sealing device is readily removable for the purpose of loadingand/or unloading the refining vessel.

It is preferred that the flame formed on ignition of the fuel/oxygenmixture is disposed within said refining vessel so that the products ofcombustion but not the flame itself impinge upon the melt. Thecarbonaceous fuel may be aliquid such as fuel oil and a proportion offinely divided particulate solids material may be entrained in saidliquid in a slurry. Typical solids materials are limestone and iron ore.

Following is a description with reference to the accompany ing drawingsof a particular converter hood and lance assembly for carrying thepresent invention into effect.

It will be appreciated that the system to be described with reference tothe accompanying drawings is by way of example only and a combination offurnace, lance and the like other than that described below may be usedin the method of the present invention. In the drawings:

FIG. 1 is a part sectional view of a converter and exhaust systemassembly in accordance with the present invention;

FIG. 2 is a plan view of the sealing device and converter of FIG. 1;

FIG. 3 is a fragmentary view of the converter and sealing device andhood assembly shown in FIG. 1; and

FIG. 4 is a fragmentary view on a much enlarged scale of the lance shownin FIG. 11.

A refining vessel 11 is supported in an upright position and is providedtowards its lower end with a taphole 12 for removal of the refined metaltherefrom and the second taphole 13 for the removal of slag at the endof a blow. The converter is open at its upper end 15 and is providedwith an annular lip 14 which forms a ring concentric with andperpendicular to the vertical median line of the converter. Theconverter is suitably lined with a known manner.

Encircling the upper end of the converter vessel 11 is an annularsealing rig 16 having a radially extending upper face 17 which slopesslightly downwards the front portion of its width and then continuesdown as at 18 but more abruptly to form the upper part of ring 16 of adouble frustoconical configuration. The outer and more downwardlysloping face 18 is adapted to form a seal as will hereinafter bedescribed. The remaining lower portion of ring 16 is in the form of adepending skirt 19 which with diverging sides complementary to thecontiguous outer surface of converter vessel 11 to which it is fixedlyattached by rivetting or other suitable means.

Coaxial with the vessel 11 is a refractory-lined hood 20 communicatingwith an exhaust duct 107. The hood 20 is of frustoconical form and has acircular transverse section and converges in a direction upwardly fromthe converter 11. The hood 20 accommodates a pressure-sensing device1104 extending through the wall and the refractory lining of hood 20 forthe purpose hereinafter described.

The hood 20 carries about its lower peripheral edge a sealing ring 21which is attached thereto in a manner similar to the fastening of ring16 above the upper end of converter vessel 1 1, said ring 16 having aconcentric sloping face 22 which is in symmetry with the face 18 withreference both to the vertical centerline of the vessel 11 and to thehorizontal plane bisecting the space intermediate these confrontingfaces.

The space between the vessel 11 and the hood 20 is provided to allow thevessel to pivot about a horizontal axis without interference should thisbe the selected manner of charging and discharging the contents of thevessel 1 1.

In order to maintain the gases issuing from the vessel 11 substantiallyout of contact with the air or atmosphere, said space is arranged to beclosed so as to be substantially gastight and to enable handling of suchgases at high temperatures. A two-part sealing member 23 is providedeach part of which detachably abuts the vessel 11 at lip 14 thereof andthe surface 22 of the hood 20. Sealing member 23 has the general form ofa relatively short open-ended cylinder separated into two equalsemicylindrical parts on a vertical median plane, the two parts beingadapted to horizontal motion and having their confronting faces 24 incontact in the closed or blowing position and being spaced apartequidistant from the vertical centerline of the vessel in the retractedposition. A recess 25 has been provided in the inner wall of the sealingmember for the reception of a refractory lining 26. The upper and loweredges of the sealing member 23 are bevelled to form sealing faces 27 and28 complementary thereto and adapted to cooperate with the faces 22 and18 respectively thereby forming a seal which confines the space betweenthe opening of the vessel 11 and the entrance to the hood 20. Theabutting surfaces 24 of the sections of the sealing member 23 areprovided with mating tongues and grooves 29 and 30 respectively. It willbe apparent that when the two sections of the sealing member 23 arebrought tightly together in clamping relationship, escape of gasgenerated within the furnace to the atmosphere at this point would besubstantially precluded.

The sealing device 23 may be provided with interconnected cord passages32 which are in communication with a source of water supply anddischarge means (not shown) whereby cooling water may be circulatedwithin device 23 during the blowing period to cool the device andmaintain a more uniform temperature.

In the closed position of the sealing device 23, the inner surface ofthe refractory lining 26 is offset outwardly relative to the inner edge25 and the opening 15 in the vessel 11. During the blowing period, thesections of the sealing member are held tightly together and in sealingand clamping contact with the vessel 11 and hood by means of pressureexerted by fluid-controlled cylinders 43 of a conventional type. Thesections of the sealed member 23 are provided with flange wheels 44adapted to roll on tracks 45 straddling vessel 11' and cooperatingtherewith to maintain the alignment of said sections in their respectivepositions. The weight of the sections, tracks and operating mechanism issupported by suitable structural members such as has been indicated byreference numeral 46.

The upper end of hood 20 is connected by a duct 107 to a spark box 101which during the blowing period serves to remove from duct 107 anyparticles of molten slag and metal which splash out of the convertervessel 11. The duct 107 extends into a vertical stack 109 having watersprays 103 disposed therein so that a stream or spray of water passesdownwardly of the stack, countercurrent to the flow of exhaust gasestherein. A drain 102 at the lower end of the stack serves to remove thewashing water therefrom. At the same time, the water sprays 103 serve toreduce the temperature of the gases extracted from the converter vessel11.

It is, of course, desirable to maintain a predetermined pressure in thehood so as to avoid the ingress of any air in the atmosphere which mayincrease the oxygen present at the commencement of the blow. Thispressure control is effective by means of a pressure controller 106which is connected to pressure element 104 disposed in the surface ofhood 20 as referred to above. The pressure controller acts to operate aflow control valve 105 in the water supply line to the sprays 103 instack 109. In this way, the water supply is controlled so as to vary thebuoyancy of the gases in the stack thereby controlling the pressure inthe hood 20 and mouth 15 of converter vessel 11.

The stream of fuel/oxygen mixture is introduced into the converter bymeans of a lance 110 a detail of which is more fully illustrated in FIG.4 of the accompanying drawings.

The lance 110 comprises an elongate body member 111 which is providedwith a combined delivery and burner nozzle 112 at the lower end thereof.The interior of the body member 111 of the lance 110 is built up of anumber of annular passageways or conduits by which oxygen and fuel oilare supplied to a plurality of discharge orifices 113 formed in thecombined delivery and burner nozzle 112. A fuel oil supply conduitcomprising a copper pipe 114 is preferably located centrally of the bodymember 111 of the lance 110. A plurality of supply pipes 116 are weldedas at 115 to the lower end of the pipe 114 and extend downwardlytherefrom, the pipe 116 corresponding in number to the number ofdischarge orifices 113 as will be hereinafter described.

An oxygen supply conduit comprises a pipe 117 forming an annularpassageway 118 around the oil supply pipe 1 14 to permit the free flowof oxygen downwardly towards the combined delivery and burned nozzle 112of the lance. The lower end of the oxygen supply pipe 117 extends beyondthe lower end of the oil supply pipe 114, so that a portion of each ofthe fuel oil supply pipe 114, so that a portion of each of the fuel oilsupply pipes 116 is located within the oxygen supply pipes 117. Thelower end of the oxygen supply pipe 1 17 is connected, for example bywelding as at 119, to a discharge head 120 from which extends aplurality of oxygen supply pipes 121 located at an angle to the mainlongitudinal axis of the lance, for example at an angle of about 14.

in the preferred arrangement the lance is provided with six dischargeorifices 113 and the oxygen supply conduit 117 is provided with sixcorresponding supply pipe lines 121 for the simultaneous discharge ofsix streams of oxygen at an angle to the longitudinal axis of the lance.The oil supply pipes 1 16 which extend downwardly from the lower end ofthe main oil supply conduit 114 extend in a cluster into the dischargehead of the oxygen supply pipe 117 and are then bent outwardly at 122 sothat their outer ends 123 are each located in a corresponding oxygensupply pipe 121. The arrangement is such that the six streams .of oxygenpass through the corresponding supply pipes 121 to the dischargeorifices 113 in the form of annular streams around the ends 123 of theoil supply pipes 116. The movement of the oxygen through the supplypipes 121 to the discharge orifices 113 ensures the entrainment of thefuel oil in the streams of oxygen when the lance 110 is being used as aburner.

Each of oxygen supply pipes 121 incorporates a venturi 133 the throat ofwhich is disposed intermediate the point of communication of supply pipe121 with the oxygen supply conduit 117 and the discharge orifice 113 ofsupply pipe 121. Each venturi has its throat disposed rearwardly of thedischarge point of the fuel pipe located in the oxygen supply pipe 121to provide maximum gas velocity passed the end of the fuel pipe 123debouching within supply pipe 121.

The forward converging frustoconical surface of the venturi 133 isinclined at an angle of 13 to the axis of the pipe while the rearwarddiverging frustoconical surface of the pipe is inclined at an angle of7.

The venturi serves to accelerate the oxygen supplied through supply pipe121 to a sonic velocity with a result that fuel leaving the end of thepipe 123 disposed within pipes 121 is atomized by the sonic flow ofoxygen gas passing the end of the pipe to produce intimate mixing of thefuel and oxygen prior to combustion externally of the lance afterleaving nozzle orifices 133.

The main oil supply conduit 114 is mounted for movement within the bodymember 111 of the lance 110 so that it can be adjusted upwardly ordownwardly along the longitudinal axis of the lance. In this way theposition of the ends 123 of the oil supply pipes 116 in the oxygensupply pipes 121 can be varied and this gives a certain amount of flameadjustment for the lance 110 and when it is being used as a burner.

The outer casing which forms the body 111 of the lance extends aroundthe oxygen supply conduit 117 and is flared outwardly at its lower endas at 124 to accommodate the outwardly directed oxygen supply pipes 121.The discharge and burner nozzle 112 is welded as at 125 to the flaredouter end 126 of the outer casing of the body 111 of the lance and 111nozzle 112 is dome shaped in construction and is provided as previouslymentioned with the six spaced discharge orifices 113 to which the oxygensupply pipes 121 communicate.

The annular space 127 provided between the outer casing of the elongatebody member 111 of the lance 110 and the outer surface of the oxygensupply conduit 117 is conveniently used for the supply of cooling fluidsuch as water. To this end the space is divided into two annularpassageways 128, 129 by a further annular conduit 130 and the coolingwater flows downwardly in passageway 128 through the elongate bodymember 111 around the outer surface of the oxygen supply conduit 117into the discharge burner nozzle 112 of the lance and then returnsupwardly through the annular passageway 129 formed adjacent the outercasing of the lance. The lower end 131 of conduit 130 is also flaredoutwardly to accommodate the oxygen supply pipes 121. v

The lance 110 enters the refining apparatus through the top surface ofthe cranked part of duct 107, passes coaxially of the hood '20 and thesealing means 23 into the converter vessel 1 1.

Means (not shown) are provided for raising and lowering the lance 1relative to the converter 1 1.

In operation, with the lance 110 withdrawn from the converter 11, andthe sealing elements 23 in their retracted positions, the converter 11is tilted about its axis and is charged with hot metal. The converter 11is returned to its vertical position, the sealing elements 23 are movedto their closed or clamping positions so that the edges of the sealingelements 23 abut or make contact with the sealing ring 16 and 21respectively. The lance 110 is then lowered into the furnace until thenozzle end 13 of the lance 110 is spaced from the upper surface of themelt. Oxygen is first passed down the appropriate conduit of the lanceand the fuel oil supply is turned on. The fuel oil/oxygen mixtureignites by itself and the proportion of fuel to oxygen are adjusted toproduce the desired flame. The position of the lance 110 within thevessel 11 is further adjusted so that the products of combustion but notthe flame itself impinge upon the surface of the melt.

After ignition, the proportion of oxygen is rapidly increased until anexcess of oxygen is passing into the refining vessel. The products ofthe refining reaction pass out of the mouth 15 of the converter 11 intothe hood and through duct 107 to stack 109. Splashes of .metal and slagpassing out of converter 11 with the gases are retained in spark box101. The remaining gases pass to stack 109 and travel up the stack 109against the water sprays 103 which remove dust and cool the gases whichthen pass out into the atmosphere.

During the blow, the lance 110 may be raised or lowered within theconverter 11 always provided that the flame itself does not impinge uponthe surface of the melt. During the course of the blow, a fluxing agentsuch as powdered limestone may be introduced into the converter 11 withthe fuel oil passing down the lance 110. The slag formed during the blowfloats on the top of the melt and the nozzle of the lance 110 may infact be dipping within the slag itself. The force of the gases beingemitted from the lance penetrate the slag layer and may cause adepression in the melt surface. At the end of the blow, the lance l 10is retracted upwardly of the converter the refined metal may be tappedby a taphole 12 from the base of the converter 11 while slag is removedfrom taphole 13. Alternatively, the sealing devices 23 may be retractedfrom the mouth 15 of the converter 11 and the converter vessel 11 may betilted about is axis to teem the molten metal.

The method and apparatus described above has the advantage that ignitionof the fuel oil/oxygen mixture is certain and may be permitted to takeplace with the hood and sealing device in the fully closed position.

The control of the water sprays may be in accordance with presetarrangements to maintain a desired pressure in the hood and preferablythis pressure is slightly below, for example a few millimeters below,atmospheric pressure.

1 claim:

1. Apparatus for the refining of molten metals comprising in combinationa refining vessel, a hood connected to the end of a has exhaust ductdisposed over an aperture in the vessel, sealing means for connectingthe aperture and hood to prevent substantial escape of gases passingfrom the vessel to the hood and one or more nozzles disposed within thesaid vessel and adapted to provide a stream of oxygen and carbonaceousfuel, stack means in flow combination with the hood, spray meansdisposed to spray water into the gas flow from the hood and apressure-responsive element mounted within the hood and operablyconnected to a pressure controller adapted to operate a flow conn'olvalve in the water supply to the sprays, whereby the buoyancy of thegases within the stack may be varied blyigontrolling the water splrayswithin the stack thereby contro g the pressure in the cod at the mouthof the refining vessel.

2. Apparatus as claimed in claim 1 wherein the hood is provided with amovable sealing skirt and arranged so as to close the gap between thelower edge of the hood and the mouth of the refining vessel.

3. Apparatus as claimed in 2, wherein the sealing skirt comprises aplurality of sealing elements each movable laterally of the refiningvessel from an open to a closed position in which said element contactsthe lower peripheral edge of the hood and the mouth of the refiningvessel.

4. Apparatus as claimed in claim 3, wherein the sealing skirt iscylindrical and consists of two semicylindrical portions each arrangedfor retraction in a horizontal plane to disengage from the peripheraledges of said hood and said vessel.

5. Apparatus as claimed in claim 4, wherein a first sealing ring isprovided around the aperture'of the refining vessel and a second sealingring is provided around the hood, the sealing device being arranged sothat the lower edge thereof is capable of detachably engaging the firstsealing ring and the upper edge thereof is capable of detachablyengaging the second sealing ring so that in the engaged position thesealing device provides a continuation of the hood and duct to conductgases from the refining vessel via the sealing device and hood to theduct.

6. Apparatus as claimed in 1, means for introducing a stream of oxygenand carbonaceous fuel into the converter or furnace comprises one ormore nozzles each having a body member provided with a fuel supplyconduit centrally located therein, and an oxygen supply conduitsurrounding said fuel supply conduit to provide an annular passagewayfor the supply of oxygen, wherein the body member is provided with adelivery nozzle at one end thereof formed with at least one dischargeorifice communicating with said oxygen supply conduit through an oxygensupply pipe and incorporating means for accelerating gas flow in saidoxygen supply pipe and wherein the fuel supply conduit is provided atits outlet with a fuel supply pie extending therefrom and each havingits end portion situated in the oxygen supply pipe so that oxygenflowing from said supply pipe to the discharge orifice will flow in anannulus around the end of the corresponding fuel supply pipe wherebyfuel will be entrained in the oxygen supply when discharged from thedischarge orifices.

7. Apparatus as claimed in claim 6, wherein each nozzle comprises aplurality of discharge orifices each communicating with said oxygensupply conduit through a plurality of oxygen supply pipes disposed at anangle to the longitudinal axis of the body and wherein a plurality offuel supply pipes extend from the fuel supply conduit each having itsend portion situated in a corresponding oxygen supply pipe.

8. Apparatus as claimed in claim 7, wherein the body member is providedwith cooling means in the form of annular passageways surrounding theoxygen supply conduits.

9. Apparatus as claimed in claim 8, wherein the means for acceleratinggas flow in the oxygen supply pipes comprises a venturi, the area of thethroat of said venturi being determined by the velocity required foroxygen leaving the nozzle.

10. Apparatus as claimed in claim 9, wherein the converging section ofeach venturi in the direction of gas flow is at an angle of and whereinthe diverging section is at an angle of 7 each to the longitudinal axisof the oxygen supply pipe.

2. Apparatus as claimed in claim 1 wherein the hood is provided with amovable sealing skirt and arranged so as to close the gap between thelower edge of the hood and the mouth of the refining vessel. 3.Apparatus as claimed in 2, wherein the sealing skirt comprises aplurality of sealing elements each movable laterally of the refiningvessel from an open to a closed position in which said element contactsthe lower peripheral edge of the hood and the mouth of the refiningvessel.
 4. Apparatus as claimed in claim 3, wherein the sealing skirt iscylindrical and consists of two semicylindrical portions each arrangedfor retraction in a horizontal plane to disengage from the peripheraledges of said hood and said vessel.
 5. Apparatus as claimed in claim 4,wherein a first sealing ring is provided around the aperture of therefining vessel and a second sealing ring is provided around the hood,the sealing device being arranged so that the lower edge thereof iscapable of detachably engaging the first sealing ring and the upper edgethereof is capable of detachably engaging the second sealing ring sothat in the engaged position the sealing device provides a continuationof the hood and duct to conduct gases from the refining vessel via thesealing device and hood to the duct.
 6. Apparatus as claimed in 1, meansfor introducing a stream of oxygen and carbonaceous fuel into theconverter or furnace comprises one or more nozzles each having a bodyMember provided with a fuel supply conduit centrally located therein,and an oxygen supply conduit surrounding said fuel supply conduit toprovide an annular passageway for the supply of oxygen, wherein the bodymember is provided with a delivery nozzle at one end thereof formed withat least one discharge orifice communicating with said oxygen supplyconduit through an oxygen supply pipe and incorporating means foraccelerating gas flow in said oxygen supply pipe and wherein the fuelsupply conduit is provided at its outlet with a fuel supply pieextending therefrom and each having its end portion situated in theoxygen supply pipe so that oxygen flowing from said supply pipe to thedischarge orifice will flow in an annulus around the end of thecorresponding fuel supply pipe whereby fuel will be entrained in theoxygen supply when discharged from the discharge orifices.
 7. Apparatusas claimed in claim 6, wherein each nozzle comprises a plurality ofdischarge orifices each communicating with said oxygen supply conduitthrough a plurality of oxygen supply pipes disposed at an angle to thelongitudinal axis of the body and wherein a plurality of fuel supplypipes extend from the fuel supply conduit each having its end portionsituated in a corresponding oxygen supply pipe.
 8. Apparatus as claimedin claim 7, wherein the body member is provided with cooling means inthe form of annular passageways surrounding the oxygen supply conduits.9. Apparatus as claimed in claim 8, wherein the means for acceleratinggas flow in the oxygen supply pipes comprises a venturi, the area of thethroat of said venturi being determined by the velocity required foroxygen leaving the nozzle.
 10. Apparatus as claimed in claim 9, whereinthe converging section of each venturi in the direction of gas flow isat an angle of -* and wherein the diverging section is at an angle of 7*each to the longitudinal axis of the oxygen supply pipe.